scholarly journals Non-Linear Damping of Surface Alfvén Waves Due to Uniturbulence

2022 ◽  
Vol 8 ◽  
Author(s):  
Rajab Ismayilli ◽  
Tom Van Doorsselaere ◽  
Marcel Goossens ◽  
Norbert Magyar
Keyword(s):  
Magnetic Field ◽  
Alfven Waves ◽  
Equilibrium Density ◽  
Alfvén Waves ◽  
Constant Density ◽  
Analytical Prediction ◽  
Background Magnetic Field ◽  
Kink Waves ◽  
Linear Damping ◽  
Analytical Expressions

This investigation is concerned with uniturbulence associated with surface Alfvén waves that exist in a Cartesian equilibrium model with a constant magnetic field and a piece-wise constant density. The surface where the equilibrium density changes in a discontinuous manner are the source of surface Alfvén waves. These surface Alfvén waves create uniturbulence because of the variation of the density across the background magnetic field. The damping of the surface Alfvén waves due to uniturbulence is determined using the Elsässer formulation. Analytical expressions for the wave energy density, the energy cascade, and the damping time are derived. The study of uniturbulence due to surface Alfvén waves is inspired by the observation that (the fundamental radial mode of) kink waves behave similarly to surface Alfvén waves. The results for this relatively simple case of surface Alfvén waves can help us understand the more complicated case of kink waves in cylinders. We perform a series of 3D ideal MHD simulations for a numerical demonstration of the non-linearly self-cascading model of unidirectional surface Alfvén waves using the code MPI-AMRVAC. We show that surface Alfvén waves damping time in the numerical simulations follows well our analytical prediction for that quantity. Analytical theory and the simulations show that the damping time is inversely proportional to the amplitude of the surface Alfvén waves and the density contrast. This unidirectional cascade may play a role in heating the coronal plasma.

scholarly journals Large-amplitude electromagnetic waves in magnetized relativistic plasmas with temperature

2014 ◽  
Vol 21 (1) ◽  
pp. 217-236 ◽  
Author(s):  
V. Muñoz ◽  
F. A. Asenjo ◽  
M. Domínguez ◽  
R. A. López ◽  
J. A. Valdivia ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Thermal Effects ◽  
Large Amplitude ◽  
Plasma Frequency ◽  
Plasma Temperature ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Background Magnetic Field ◽  
Cold Case ◽  
Effective Plasma Frequency

Abstract. Propagation of large-amplitude waves in plasmas is subject to several sources of nonlinearity due to relativistic effects, either when particle quiver velocities in the wave field are large, or when thermal velocities are large due to relativistic temperatures. Wave propagation in these conditions has been studied for decades, due to its interest in several contexts such as pulsar emission models, laser-plasma interaction, and extragalactic jets. For large-amplitude circularly polarized waves propagating along a constant magnetic field, an exact solution of the fluid equations can be found for relativistic temperatures. Relativistic thermal effects produce: (a) a decrease in the effective plasma frequency (thus, waves in the electromagnetic branch can propagate for lower frequencies than in the cold case); and (b) a decrease in the upper frequency cutoff for the Alfvén branch (thus, Alfvén waves are confined to a frequency range that is narrower than in the cold case). It is also found that the Alfvén speed decreases with temperature, being zero for infinite temperature. We have also studied the same system, but based on the relativistic Vlasov equation, to include thermal effects along the direction of propagation. It turns out that kinetic and fluid results are qualitatively consistent, with several quantitative differences. Regarding the electromagnetic branch, the effective plasma frequency is always larger in the kinetic model. Thus, kinetic effects reduce the transparency of the plasma. As to the Alfvén branch, there is a critical, nonzero value of the temperature at which the Alfvén speed is zero. For temperatures above this critical value, the Alfvén branch is suppressed; however, if the background magnetic field increases, then Alfvén waves can propagate for larger temperatures. There are at least two ways in which the above results can be improved. First, nonlinear decays of the electromagnetic wave have been neglected; second, the kinetic treatment considers thermal effects only along the direction of propagation. We have approached the first subject by studying the parametric decays of the exact wave solution found in the context of fluid theory. The dispersion relation of the decays has been solved, showing several resonant and nonresonant instabilities whose dependence on the wave amplitude and plasma temperature has been studied systematically. Regarding the second subject, we are currently performing numerical 1-D particle in cell simulations, a work that is still in progress, although preliminary results are consistent with the analytical ones.

scholarly journals Filamentary Alfvénic structures excited at the edges of equatorial plasma bubbles

2007 ◽  
Vol 25 (10) ◽  
pp. 2159-2165 ◽  
Author(s):  
R. Pottelette ◽  
M. Malingre ◽  
J. J. Berthelier ◽  
E. Seran ◽  
M. Parrot
Keyword(s):  
Alfven Waves ◽  
Alfvén Waves ◽  
Plasma Bubble ◽  
Plasma Bubbles ◽  
Wave Measurements ◽  
Demeter Satellite ◽  
Equatorial Plasma Bubbles ◽  
Background Magnetic Field ◽  
Gravity Driven ◽  
Displacement Currents

Abstract. Recent observations performed by the French DEMETER satellite at altitudes of about 710 km suggest that the generation of equatorial plasma bubbles correlates with the presence of filamentary structures of field aligned currents carried by Alfvén waves. These localized structures are located at the bubble edges. We study the dynamics of the equatorial plasma bubbles, taking into account that their motion is dictated by gravity driven and displacement currents. Ion-polarization currents appear to be crucial for the accurate description of the evolution of plasma bubbles in the high altitude ionosphere. During their eastward/westward motion the bubbles intersect gravity driven currents flowing transversely with respect to the background magnetic field. The circulation of these currents is prohibited by large density depressions located at the bubble edges acting as perfect insulators. As a result, in these localized regions the transverse currents have to be locally closed by field aligned currents. Such a physical process generates kinetic Alfvén waves which appear to be stationary in the plasma bubble reference frame. Using a two-dimensional model and "in situ" wave measurements on board the DEMETER spacecraft, we give estimates for the magnitude of the field aligned currents and the associated Alfvén fields.

scholarly journals Multifrequency compressional magnetic field oscillations and their relation to multiharmonic toroidal mode standing Alfvén waves

2015 ◽  
Vol 120 (12) ◽  
pp. 10,384-10,403 ◽  
Author(s):  
Kazue Takahashi ◽  
Colin Waters ◽  
Karl-Heinz Glassmeier ◽  
Craig A. Kletzing ◽  
William S. Kurth ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Toroidal Mode

Concerning the Dynamics of Energetic Protons in Coronal Magnetic Loops: Dispersion Effects of Alfven Waves

1985 ◽  
Vol 107 ◽  
pp. 559-559
Author(s):  
V. A. Mazur ◽  
A. V. Stepanov
Keyword(s):  
Magnetic Field ◽  
Wave Dispersion ◽  
Alfven Waves ◽  
Alfven Wave ◽  
Wave Number ◽  
Alfvén Waves ◽  
Coronal Loops ◽  
Coronal Magnetic Loops ◽  
The Magnetic Field ◽  
Solar Coronal

It is shown that the existence of plasma density inhomogeneities (ducts) elongated along the magnetic field in coronal loops, and of Alfven wave dispersion, associated with the taking into account of gyrotropy U ≡ ω/ωi ≪ 1 (Leonovich et al., 1983), leads to the possibility of a quasi-longitudinal k⊥ < √U k‖ propagation (wave guiding) of Alfven waves. Here ω is the frequency of Alfven waves, ωi is the proton gyrofrequency, and k is the wave number. It is found that with the parameter ξ = ω2 R/ωi A > 1, where R is the inhomogeneity scale of a loop across the magnetic field, and A is the Alfven wave velocity, refraction of Alfven waves does not lead, as contrasted to Wentzel's inference (1976), to the waves going out of the regime of quasi-longitudinal propagation. As the result, the amplification of Alfven waves in solar coronal loops can be important. A study is made of the cyclotron instability of Alfven waves under solar coronal conditions.

scholarly journals Alfvén Waves in Dusty Interstellar Clouds

1997 ◽  
Vol 14 (2) ◽  
pp. 170-178 ◽  
Author(s):  
N. F. Cramer ◽  
S. V. Vladimirov
Keyword(s):  
Magnetic Field ◽  
Negative Charge ◽  
Alfven Waves ◽  
Dust Particles ◽  
Alfvén Waves ◽  
Interstellar Clouds ◽  
General Dispersion ◽  
The Right ◽  
The Magnetic Field ◽  
Field Wave

AbstractDust particles in a plasma can be higWy charged, and can carry a proportion of the negative charge of the plasma. Even if this proportion is quite small, as in interstellar dusty clouds, it can have a large effect on hydromagnetic Alfvén waves propagating at frequencies well below the ion–cyclotron frequency. In particular, the right-hand circularly polarised mode experiences a cutoff due to the presence of the dust. We generalise previous work on Alfvén waves in dusty interstellar plasmas by considering the general dispersion relation for waves propagating at an arbitrary angle with respect to the magnetic field. Wave energy propagating at oblique angles to the magnetic field in an increasing density gradient can be very efficiently damped by the Alfvén resonance absorption process in a dusty plasma, and we consider this damping mechanism for waves in interstellar clouds.

Effect of the magnetic field curvature on the generation of zonal flows by drift-Alfvén waves

2007 ◽  
Vol 33 (5) ◽  
pp. 407-419 ◽  
Author(s):  
A. B. Mikhailovskii ◽  
E. A. Kovalishen ◽  
M. S. Shirokov ◽  
V. S. Tsypin ◽  
R. M. O. Galvão
Keyword(s):  
Magnetic Field ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Zonal Flows ◽  
Field Curvature ◽  
The Magnetic Field

scholarly journals Relativistic Alfvén Waves on the jet of BL Lacertae

2014 ◽  
Vol 10 (S313) ◽  
pp. 147-152
Author(s):  
Marshall H. Cohen ◽  
David L. Meier
Keyword(s):  
Magnetic Field ◽  
Pitch Angle ◽  
Lorentz Factor ◽  
Alfven Waves ◽  
Longitudinal Component ◽  
Mhd Waves ◽  
Alfvén Waves ◽  
Bl Lacertae ◽  
Pattern Speeds ◽  
Helical Magnetic Field

AbstractThe jet of BL Lac displays transverse patterns that propagate downstream superluminally. We suggest that they are transverse Alfvén waves propagating on the longitudinal component of a helical magnetic field. The speed of the wave adds relativistically to the speed of the beam, and the apparent speed of the pattern is greater than the beam speed. Models for the jet and the MHD waves give values for the Lorentz factor of the beam of 3–4.4 and pitch angle of the helical magnetic field of 43° - 65°. These are consistent with other estimates, if the beam and pattern speeds are allowed to differ.

scholarly journals Concerning the Dynamics of Energetic Protons in Coronal Magnetic Loops: Dispersion Effects of Alfven Waves

1985 ◽  
Vol 107 ◽  
pp. 559-559
Author(s):  
V. A. Mazur ◽  
A. V. Stepanov
Keyword(s):  
Magnetic Field ◽  
Wave Dispersion ◽  
Alfven Waves ◽  
Alfven Wave ◽  
Wave Number ◽  
Alfvén Waves ◽  
Coronal Loops ◽  
Coronal Magnetic Loops ◽  
The Magnetic Field ◽  
Solar Coronal

It is shown that the existence of plasma density inhomogeneities (ducts) elongated along the magnetic field in coronal loops, and of Alfven wave dispersion, associated with the taking into account of gyrotropy U ≡ ω/ωi ≪ 1 (Leonovich et al., 1983), leads to the possibility of a quasi-longitudinal k⊥ < √U k‖ propagation (wave guiding) of Alfven waves. Here ω is the frequency of Alfven waves, ωi is the proton gyrofrequency, and k is the wave number. It is found that with the parameter ξ = ω2 R/ωi A > 1, where R is the inhomogeneity scale of a loop across the magnetic field, and A is the Alfven wave velocity, refraction of Alfven waves does not lead, as contrasted to Wentzel's inference (1976), to the waves going out of the regime of quasi-longitudinal propagation. As the result, the amplification of Alfven waves in solar coronal loops can be important. A study is made of the cyclotron instability of Alfven waves under solar coronal conditions.

Sign in / Sign up

Export Citation Format

Share Document